linux-kernel - Re: [PATCH v3 1/2] media: venus: fix TOCTOU vulnerability when reading packets from shared memory

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Message-ID: <bd704149-694f-4d89-90d9-a22307488743@linaro.org>
Date: Thu, 15 May 2025 13:47:12 +0100
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: Vikash Garodia <quic_vgarodia@...cinc.com>,
 Dikshita Agarwal <quic_dikshita@...cinc.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Stanimir Varbanov <stanimir.varbanov@...aro.org>,
 Hans Verkuil <hans.verkuil@...co.com>
Cc: linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 linux-kernel@...r.kernel.org, Vedang Nagar <quic_vnagar@...cinc.com>
Subject: Re: [PATCH v3 1/2] media: venus: fix TOCTOU vulnerability when
 reading packets from shared memory

On 15/05/2025 13:11, Vikash Garodia wrote:
>> But what if the "malicious" firmware only updated the data in the packet, not
>> the length - or another field we are not checking ?
> That does not cause any vulnerability. You can check and suggest if you see a
> vulnerability when the data outside length is an issue w.r.t vulnerability.

I don't believe you have identified a vulnerability here.

You read a length field, you check that length field against a MAX size.

Re-reading to see if the firmware wrote new bad data to the transmitted 
packet in-memory is not a fix before or after the memcpy() because the 
time you do that re-read is not fixed - locked wrt the freerunning firmware.

---
bod